Ionic method for hydrogenating

The so-called ionic method for hydrogenating thiophenes (78T1703) is a further illustration of the chemical consequences of protonation. Protonation of the thiophene ring renders the ring susceptible to hydride ion attack, conveniently derived from triethylsilane (Scheme 12). 

The chemical shift differences of the diastereotopic hydrogens are listed in Table 17 they depend strongly on solvent effects, as expected for an ionic product. They are in the range of 8 = 0.01 -0.1, well suited for measurement of the enantiomeric purity of the phosphanes. An alternative method for the measurement of Horner phosphanes is by 13C-NMR spectroscopy of diastereomeric complexes formed with [>/3-( + )-0 7 ,57 )-pinenyl]nickel bromide dimer73. 

The last of the direct methods for graft initiation in liquid phase presented in this review involves chemical additives. Either free radical or ionic initiators can be chosen. Benzoyl peroxide is reported for grafting styrene on Nylon fibers in methanol media (71,105-107), as well as vinyl acetate (106). Azoisobutyro-nitrile has been employed in systems where the graft monomer is styrene (71,106) or vinyl acetate (106). Redox systems involving hydrogen peroxide and monomers like styrene (106,108,109). vinyl acetate (106), acrylic acid (108,109), methyl... 

The tin hydride method is reductive, and the cyclic radical is almost always trapped by a hydrogen atom. In simple cyclizations, both the radical precursor and the alkene are lost during tin hydride reduction, and this sometimes results in underfunctionalized products, necessitating the introduction of extra functional groups for subsequent transformations. However, in the synthesis of simple molecules, this is often an advantage as steps to remove residual alkenes, carbonyl groups and the like, left by ionic methods of C—C bond formation, are not required. Work-up requires separation of the desired products from the tin by-products (see Section 4.1.6.2.1). 

Pryor WA, Cueto R, Koppenol WEI, Ngu-Schwemlein M, Squadrito GL, Uppu PL, Uppu RM (1995) A practical method for preparing peroxynitrite solutions of low ionic strength and free of hydrogen peroxide. Free Rad Biol Med 18 75-83... 

Pyrolysis of steroid esters, particularly benzoates, has been used as a method for the preparation of olefins [143]. The reaction involves a cis hydrogen atom stereospecifically and is interpreted in terms of a cyclic transition state of essentially non-ionic character (i). The specificity of the reaction is such that 5a-cholestan-4jS yl benzoate (2) gave only the A -olefin (3) [118], whereas the epimeric 4a-benzoate (4) gave the... 

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